In the following description and explanation of this invention, reference will be made primarily to the lining of underground sewers, though it is to be understood that the pipe construction system of this invention is not limited to this application, and may be used for a very wide range of different applications. For example, the system may be used to construct an overland or underground pipe, as well as to line a wide variety of ducts, so long as the duct is sufficiently large to permit access by human operators, to effect the lining method.
Many underground sewers in major cities throughout the world were constructed more than 100 years ago. Consequently, those sewers are by now becoming very worn internally, with the brickwork or other constructional materials deteriorating in view of the nature of the liquids and gases present within the sewer. Further, due to ground movements over the years, the structural integrity of those sewers can be seriously compromised. These aspects can lead to failure within sewers, by the walls of the sewers collapsing inwardly. The consequent remedial work necessary to restore the sewer is extremely difficult and unpleasant to perform, since by the time such work is commenced, there is likely to be a large volume of sewage backed up behind a blockage caused by the failure.
It is known to provide a lining within underground ducts such as sewers, in an attempt to restore integrity to the structure. Such a lining technique may be performed before there is a catastrophic failure, by opening the sewer at a convenient point and then fitting into the sewer relatively short lengths of pipe which are connected together end-to-end. In the case of a sewer of circular cross-sectional shape, such short lengths of a pipe may be a sliding fit within the existing sewer so that no further work is required. Alternatively, the external diameter of the assembled pipe may be significantly less than the internal diameter of the sewer and then a grouting material is injected under pressure into the generally annular space between the pipe and the internal sewer wall.
Particularly in the case of relatively large sewers, it is also known to assemble a lining from short lengths of pipe which lengths themselves are assembled from segments each of part-circular shape. One widely used system employs a tongue along one axially-extending edge of a segment and a correspondingly formed groove along the other axially-extending edge of a segment whereby the segments may be assembled together with the tongue of one segment fitting into the groove of the next adjacent segment. This system has the disadvantage that the strength of the segments is much reduced in the area of the inter-fitting tongues and grooves resulting in a relatively weak joint between adjacent segments. Further, it is necessary axially to slide the last segment (or the second segment, where two semi-circular segments form the pipe section) into position and during this sliding movement, there is a relatively high risk that the tongue or one of the groove walls will be broken away from its segment.
An alternative but similar system uses butt or halved joints between adjacent lining segments, each of which joints is reinforced with an elongate internal cover plate secured over the joint. Such a system is slow and inconvenient to install, especially within the confined working space of a sewer.
A disadvantage of the above systems is that the strength and water-tight integrity of a pipe assembled as described is relatively low and so the systems are unsuitable for use other than in a grouted pipe-lining situation, where the strength may be enhanced by the surrounding grout and already existing duct or sewer. Even so, the joint could still leak and over a period of time and so deteriorate the integrity of the surrounding grout.
It has been proposed to strengthen the longitudinal joints between adjacent segments by enlarging the wall thickness in the region of the joints but in order to give a smooth internal surface to the finished pipe, all such enlargement must be effected externally of the pipe. However, this then gives rise to a problem at the ends of the pipe sections where the end of one pipe section forms a spigot which fits into a socket formed at the opposite end of the next adjacent pipe section. The enlarged wall thickness must be cut away and this leads to a very weak area of the assembled pipe, which also is highly likely to leak.